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On 07/05/2019 09:36 AM, Tom McDermott
via USRP-users wrote:
Hi Marcus - thanks for the link to the documentation. Messages don't have
the required functionality, so I have tried to insert tx_sob and tx_eob tags.
This unfortunately has not changed anything. This is what the tag debug shows,
are these formatted correctly for UHD USRP sink?
----------------------------------------------------------------------
Tag Debug:
Input Stream: 00
Offset: 139250 Source: burst_tagger4 Key: tx_sob Value: #t
----------------------------------------------------------------------
----------------------------------------------------------------------
Tag Debug:
Input Stream: 00
Offset: 196587 Source: burst_tagger4 Key: tx_eob Value: #t
----------------------------------------------------------------------
I have to stop streaming samples to the USRP Sink to get it to stop transmitting and
switch TX/RX over to RX - the tags aren't enough. However the next time back to Tx,
the problem with transmitter underruns and weird oscillating T/R behavior resumes.
Still looking for advice as to how to T/R switch the unit without the TX going nuts?
-- Tom, N5EG
Indeed, if there are ANY samples after a tx_eob, the USRP will go
back into transmitting mode.
I'm copying the discuss-gnuradio mailing list, since this is really
an issue of how to make tagged streams behave
as-expected with GRC-derived flow-graphs.
I've never implemented a half-duplex TX scheme out of GRC myself,
but there are folks on the discuss-gnuradio mailing list
who have.
On 07/04/2019 11:14 PM, Tom McDermott via USRP-users wrote:
> I am trying to use a B205mini in half-duplex mode through the TX/RX
> connector
> from a GRC flowgraph. Gnuradio 3.7.13.4. Very slow switching,
> manually implemented.
>
> The flowgraph implements a simple half-duplex transceiver. In order to
> switch
> the TX/RX antenna switch, I am starting and stopping samples to the
> USRP sink
> using the Copy block. When the Copy block is enabled it passes
> samples to the USRP sink,
> and when disabled it does not copy samples to the USRP sink.
>
> If the Copy block is statically enabled, then the USRP transmits (RED
> led 'On' for TX/RX)
> continuously without any underruns.
>
> If the Copy is statically disabled, then USRP goes into receive mode
> (GREEN led 'On' for TX/RX)
> and stays in that mode.
>
> So far so good.
>
> However if I toggle the enable/disable on the copy block to disable
> the TX/RX switches as it should
> from red to green, but after I re-enable the Copy block and leave it
> enabled, the TX/RX LED goes red
> for awhile, then rapidly flashes red/green/red etc. while printing
> UUUUUUU on the GRC console, then
> goes RED for about 5 seconds without underruns, then flashes RED/GREEN
> rapidly for 5 or 10 seconds
> and underruns, back and forth ad infinitum.
>
> So Copy appears not to be a good way to implement T/R switching.
>
> There is a message port on the USRP sink block. Can this be used to
> implement T/R switching?
> Is there some place that the messages that this port accepts defined?
> I cannot seem to find
> the syntax for the message definitions in the USRP documentation, so I
> must be looking in the wrong place.
>
> -- Tom, N5EG
>
>
There's some documentation here:
https://www.gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__sink.html
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